Bent and tempered glass is used extensively for vehicle side and rear windows to provide good resistance to breakage as well as to provide an aesthetically appealing shape to complement the design of the vehicle. In order to perform the bending and tempering, the glass sheet must be heated to its deformation point of about 1200.degree. F. and then bent to the required shape before being rapidly cooled in order to temper the glass. Tempering greatly increases the mechanical strength of the glass and its resistance to breakage as well as causing the glass to break into relatively small, dull pieces when broken, instead of large sharp slivers as in the case of untempered glass.
In U.S. Pat. No. 4,282,026 entitled "Apparatus for Bending and Tempering Glass", the entire disclosure of which is hereby incorporated by reference, a glass transport apparatus disclosed includes a furnace with a housing that defines a heating chamber in which glass is heated during conveyance along a roller hearth conveyor. Side slots extend through the furnace housing through which ends of elongated conveyor rolls project outwardly from the heating chamber. Continuous drive loops in the form of either chains or solid steel belts support the ends of the conveyor rolls and are slidably driven over external support surfaces extending alongside the slots to support and frictionally drive the rolls. A vacuum holder is positioned within the heating chamber above the conveyor rolls and has a downwardly facing inner surface with restricted openings spaced thereover. A vacuum is drawn within the restricted openings to receive the heated sheet of glass from the conveyor in preparation for bending. After the sheet of glass is supported on the vacuum holder a carrier mold, preferably in the form of a curved ring, is moved under the glass. Termination of the vacuum then drops the sheet of glass onto the mold ring so that the glass sags within the furnace heating chamber under the bias of gravity from its planar condition to the curved shape of the ring. The mold ring may be changed to bend different size glass to different shapes.
It is often desirable to bend some portions of the glass sheet a greater amount than other portions. Bends having a relatively small radius of curvature are most easily accomplished by heating the glass sheet to a temperature higher than that normally achieved by single conveyance through a heating chamber. If the overall temperature of the heating chamber is raised, then those portions of the rest of the glass sheet which are not so bent, are excessively heated, thereby creating excessive distortion.
Stationary auxiliary heaters may be located adjacent the plane of glass conveyance. For example, the U.S. patent to Dean et al U.S. Pat. No. 3,273,988 discloses burners which are positioned to provide localized heating of the peripheral edges of glass sheets in order to provide a hermetically sealed dual glass glazing unit. However, with a stationary heater, the only type of localized heat that can be applied to a glass sheet is a strip along the direction of conveyance.
Prior patents disclose various movable burners or heaters for localized heating. For example, the U.S. patent of Babcock U.S. Pat. No. 3,440,031 discloses movable burners that are utilized to heat peripheral edges of a pair of glass sheets. Stationary burners are also provided to locally heat straight side edges of the glass sheets. Vertically movable burners are also disclosed to provide localized heating of the curved edges of the pair of glass sheets.
Likewise, the U.S. patent of Olsen et al U.S. Pat. No. 2,964,105 discloses angularly adjustable burners which may also be laterally adjusted.
The U.S. patent of Vranken U.S. Pat. No. 3,248,517 discloses a bending system which includes upper heaters that are movable vertically and side heaters that are moved horizontally to provide local heating.
A glass tube making machine is disclosed by the U.S. patent of Hamilton U.S. Pat. No. 3,249,414 which includes a heater mounted on a carriage for movement along the elongated direction of the bed of a lathe on which glass tubes are formed.
In the U.S. patent of Keefer U.S. Pat. No. 3,395,008 burners are supported for both horizontal and vertical movement in order to provide glazing of glass articles to remove surface defects.
A machine disclosed by U.S. patent of Anderson U.S. Pat. No. 3,488,176 includes burners that are moved between various positions during manufacturing of glass tube stems.
The U.S. patent of Dichter U.S. Pat. No. 3,874,867 discloses a vial producing machine whose burner is supported for movement between two positions during manufacturing of a glass vial.
The U.S. patent of Harker U.S. Pat. No. 2,494,387 discloses a machine including burners that are moved so as to direct heat toward tubular glass blanks that are conveyed in a circular path by a conveyor. The movable heater is to reduce fuel usage.
With certain glass sheets to be bent it is desirable to locally heat at least one strip portion of each glass sheet which extends transverse the direction of conveyance without heating the rest of the sheet. This localized heating must be performed in an environment of high furnace temperature and must keep up with the rapid rates of glass sheet production.